Thin orifice swirl injector nozzle

ABSTRACT

The nozzle of a fuel injector is constructed to have a seat member and a single thin disc orifice member. A guide member affixed to the seat member guides the injector needle toward the seat in the seat member as the needle is reciprocated within the injector by pulsing the injector solenoid. Fuel is conveyed past the guide member by holes that are spaced radially outwardly from the central hole which guides the needle and that are skewed to the injector axis. As fuel passes through these skewed holes, it acquires angular momentum. The effect of this angular momentum is to increase the divergence of the column of fuel that is emitted by the single thin disc orifice member.

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to a fuel injector, particularly to theconstruction of the injector nozzle.

In a known type of fuel injector, the nozzle comprises a single thinorifice disc out of which the fuel is emitted. Within the nozzle, justupstream of the single thin orifice disc, is a valve seat member havinga centrally located seat and hole for a needle that is operated by theinjector's solenoid to open and close the hole. The needle is guided bymeans of a needle guide member that is assembled concentrically to thevalve seat member. The needle guide member contains straight holesspaced outwardly of its needle guide hole, and these straight holesprovide for the passage of fuel through the needle guide member. In thistype of injector, the single thin orifice disc controls the static fuelflow because almost all the pressure drop occurs across it.Additionally, fuel atomization is enhanced since velocity isproportional to the square root of the pressure drop across the orifice.A further attribute of this type of fuel injector is that it isgenerally lift-insensitive. The typical fuel spray pattern from thevalve is mostly a thin column that is surrounded by a fine cloud aroundthe outside.

It has now been discovered that the spray pattern can be enhancedwithout sacrificing the aforementioned advantages of a single thinorifice disc injector. This is accomplished by making the fuel holes inthe needle guide member skewed instead of straight. As fuel passesthrough the skewed holes, angular momentum is imparted to it. Eventhough the diameter of the metering orifice in the single thin orificedisc is much smaller in diameter than either the diameter on which theskewed holes lie or the diameter of the hole through the valve seatmember, there is a significant angular momentum in the fuel that passesthrough the metering orifice so that the column of fuel that exits thenozzle has significantly increased divergence. The amount of divergenceis a function of the specific design. This type of a spray pattern willgenerally be advantageous when the injector is used to spray fuel towardthe intake valve of an internal combustion engine. Yet the injectorrequires no more parts than the known injector described above.

The foregoing features and advantages of the invention, along withadditional ones, will be seen in the ensuing description and claims,which should be considered in conjunction with the accompanyingdrawings. The drawings disclose a preferred embodiment of the inventionaccording to the best mode presently contemplated for carrying out theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view, having portions sectioned away, showing afuel injector constructed in accordance with principles of theinvention.

FIG. 2 is an enlarged sectional view of the nozzle end of the injectorwith skewed holes.

FIG. 3 is a transverse cross sectional view taken in the direction ofarrows 3--3 in FIG. 2.

FIG. 4 is a cross sectional view taken in the direction of arrows 4--4in FIG. 3.

FIG. 5 is a view of another embodiment of one of the parts of theinjector.

FIG. 6 is a top view of FIG. 5.

FIG. 7 is a bottom view of FIG. 5.

FIG. 8 is a developed view taken along arrows 8--8 in FIG. 6.

FIG. 9 is a top view of still another embodiment of one of the injectorparts.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 depicts a fuel injector 10 whose nozzle 12 is constructed inaccordance with the present invention. The injector comprises an inlet14 at the end opposite nozzle 12. Fuel passes through the injector frominlet 14 to nozzle 12. The injector further includes a needle 16 that isoperated by a solenoid 17 to control the passage of fuel from nozzle 12.FIG. 2 shows the nozzle in greater detail.

Axially captured within the nozzle end of the injector are, in orderfrom upstream to downstream, a needle guide member 18, a valve seatmember 20, a thin orifice disc member 22, and a retainer member 24.Needle guide member 18 contains a central circular hole 25 that guidesneedle 16 for axial motion toward and away from a frusto-conicallyshaped seat 26 centrally located in the upper face of seat member 20.Seat 26 leads to a circular hole 28 that is concentric with the seat. Acircular orifice 30 in thin orifice disc member 22 is coaxial with hole28. Retainer member 24 contains a flared hole 32 that is sized so as notto interfere with the fuel that is emitted from orifice 30. FIG. 2 showsthe condition with solenoid 17 de-energized so that the rounded tip ofneedle 16 seats on seat 26 to close hole 28. When the solenoid isenergized, the needle unseats from the seat to open the hole

Member 18 is provided with fuel passage holes 34 that enable fuel topass through it. These holes are spaced radially outwardly of hole 25.In accordance with principles of the invention, holes 34 are skewed tothe injector axis so that when fuel passes through them, acircumferential, or angular, component of motion, i.e. swirl, isimparted to the fuel. FIGS. 3 and 4 illustrate further details of member18. Holes 34 are straight but are skewed to the injector axis. Thelength, diameter, angle of skew and the number of holes are factors thatare important in attaining a satisfactory design. The number of fuelpassages are chosen to be the minimum number to give reasonablyhomogeneous angular velocity. For a given hole length, more holes give amore homogeneous angular velocity, but since the total hole areaincreases if the total number of holes is increased, a larger number ofholes mandates that hole diameter be reduced to maintain the cone angleof the fuel spray. Small holes are less economical to produce. Testresults have shown that for most four-stroke automotive engines fourholes are the appropriate number. Failure to observe the need to keepthe total hole area under control will result in either too much swirland a very wide cone angle, or too little swirl and an extremely narrowor ineffective cone. A balance must be struck between cone angle andhole size, together with hole angle.

Another factor that influences cone angle is the length to diameterratio of the holes. A very small length to diameter ratio (approachingunity) will reduce cone angle significantly. There is no optimum ratio,since the only objective is the cone angle. Generally, the steeper (orsmaller) the hole angle, the easier the holes are to make, and thisproduces a shorter hole for a given design of member 18. Alternately,since a shorter hole produces less swirl, the hole angle will need to beincreased to achieve a given cone angle as compensation for being tooshort.

It is also important to minimize the volume of fuel that is trappedbetween members 18 and 20 when needle 16 seats on seat 26 to close hole28. It can be seen in FIG. 2 that member 18 is designed to do this. Themember is shaped with a formation that fits into the upper portion ofthe depression forming seat 26. During operation of the injector, thefuel that is below member 18 has residual angular momentum from itspassage through holes 34. This is true even for fuel that is below theseat and in the exhaust, or sack, volume. This will have the effect ofkeeping a small amount of fuel in the sack volume rather than allowingit to drip out after injection is complete. This small amount will besmaller than a conventional thin orifice injector because this outerlayer of fuel will be displaced through the thin orifice by the angularmomentum of the inner fuel.

A certain amount of fuel may flow between needle 16 and the wall of hole25. This fuel will not have swirl and must be controlled. By combiningthe needle guide function with the swirl function in the one piece,member 18, precision operations are conducted on a single piece andtolerance stack-ups that might otherwise occur are avoided.

Further advantages of the invention are that the injector is lesssensitive to injector aiming; fuel that ricochets off an engine intakevalve is generally of comparatively small particle size; fuel particlesare generally more homogeneous; the effect of the sack volume islessened; symmetry of spray is assured.

FIGS. 5, 6, 7, and 8 illustrate a further embodiment of member 18 inwhich the holes 34 are in the form of three spiral rectangular slotsthat are contiguous with guide hole 25. FIG. 9 shows still anotherembodiment in which member 18 is a powdered metal part in which theholes 34 are straight channels that are open to the circumferentiallyouter edge of the member.

While a preferred embodiment of the invention has been disclosed,principles are applicable to other embodiments.

What is claimed is:
 1. In a fuel injector which comprises an injectorbody having a fuel passage that extends axially of the injector body toa nozzle at which fuel is emitted, said nozzle comprising a seat memberhaving an upper face and a lower face, a frusto-conical depressionformed in a central region of said seat member's upper face, a hole thatextends from the bottom of said depression to the lower face of saidseat member, said fuel injector comprising a needle that is reciprocatedaxially within said fuel passage by a mechanism that includes asolenoid, said needle having a tip end that seats on and unseats fromthe bottom of said depression to close and open said hole, a needleguide member that is affixed to the upper face of said seat member andcomprises a central hole through which said needle passes for guidingsaid needle into seating on the bottom of said depression, said needleguide member further comprising fuel passage holes that extend throughthe needle guide member to convey fuel past the needle guide member, anda thin disc orifice member downstream of said seat member comprisingmetering orifice means for metering fuel emitted by the injector whenthe needle is unseated from the bottom of said depression, theimprovement which comprises said needle guide member comprising aformation that fits into an upper portion of said seat memberdepression, said formation having a lower face within said seat memberdepression, wherein said fuel passage holes of said needle guide memberhave their outlets at the lower face of said formation and wherein saidfuel passage holes of said needle guide member are skewed to theinjector axis so that a circumferential component of motion is impartedto fuel that has passed through said fuel passage holes of said needleguide member before the fuel passes through said metering orifice meansof said thin disc orifice member.
 2. The improvement set forth in claim1 wherein said fuel passage holes are spaced radially outwardly of saidcentral hole in said needle guide member.
 3. The improvement set forthin claim 1 wherein said fuel passage holes are contiguous with saidcentral hole in said needle guide member.
 4. The improvement set forthin claim 1 wherein said fuel passage holes are formed by channels thatare open to the outer circumferential edge of the needle guide member.